1. Field of the Invention
The present invention relates to a method for judging the failure or end of life of a sensor element and, in particular, to such method which is able to judge the same with accuracy.
2. Description of the Related Art
A gas sensor element is used to detect an electromotive force generated when a chemical substance contained therein reacts with a substance to be detected to thereby measure the density of the substance to be detected and the like. As the gas sensor element is used, it will deteriorate and thus it can fail or come to the end of life.
Conventionally, as a method for judging the failure or the end of life of the sensor element due to the deterioration thereof, there are known several methods, for example, a judging method using the accumulation of the operation time of a gas sensor element as disclosed in Japanese Patent Publication No. Hei. 8-233770, a judging method using the periodical proofreading of the sensor element, and the like. However, in these conventional judging methods, there are still found some problems to be solved as follows:
(1) Judging method using the accumulation of the operation time (Japanese Patent Publication No. Hei. 8-233770): Since the operation time of the gas sensor element is accumulated and measured for judgment on the failure or end of life of the gas sensor element, the accumulated operation time must be stored, which means that it is necessary to provide a device for storing the accumulated operation time. Because the judgment is made based on the operation time of the sensor element, even if the sensor element is deteriorating at an accelerated rate, the end of life thereof cannot be judged unless enough operation time has been accumulated to obtain an effective evaluation; and,
(2) Judging method using the periodical proofreading of the sensor element: In this method, the sensor element is proofread during a previously determined period using some reference source or other reference means. The deterioration of the sensor element cannot be measured during the operation period. In addition, it is necessary to prepare the reference source before proofreading the sensor element.